Conventionally, grain pests are exterminated mainly by pesticide spraying, which, however, tends to be avoided due to safety concerns. Thus, recently, many techniques have been proposed for exterminating grain pests by heating the grain (see, for example, Patent Literatures 1 and 2).
The technique described in Patent Literature 1 involves heating cereals by placing the cereals in contact with a high-temperature cylinder while the technique described in Patent Literature 2 involves heating cereals by a high-temperature gas.
The techniques described in the aforementioned patent literatures can exterminate insect pests, their larvae, their eggs, and the like which get mixed in, or parasitize, grain, by heating the grain by a high-temperature heating medium.
Now, the techniques described in the aforementioned patent literatures heat the grain for a short time by taking into consideration the influence of heat on the grain.
However, the techniques described in the aforementioned patent literatures heat the grain by a high-temperature heating medium, and cannot necessarily prevent the influence of heat on the grain by merely reducing a heating time. Consequently, there is a problem in that properties and condition of the grain will change, resulting in quality deterioration of the grain.